1. Field of the Invention
This invention relates to sewing machines, and in particular to a twin-needle sewing machine for simultaneously stitching a pair of concealed slide fastener stringers onto a desired fabric. The invention is even more particularly directed to means for guiding the fastener stringers under the needles as they are stitched onto a fabric by such a sewing machine. The term "fabric" is used herein and in the appended claims in a broad sense, to mean any material to which fastener stringers can be sewn or stitched.
2. Description of the Prior Art
For simultaneously stitching a pair of concealed slide fastener stringers onto a fabric, it has been customary to use a twin-needle sewing machine the presser foot of which has a pair of guide channels formed in its bottom face for slidably receiving the respective rows of fastener elements of the stringers. This prior art device gives rise to various problems which adversely affect the efficiency with which the concealed fastener stringers are attached to successive pieces of fabric.
First of all, prior to stitching operation, the row of elements on one of the stringers must be manipulated into the corresponding one of the guide channels in the presser foot in its raised position. With this stringer supported under the presser foot with one hand, the operator proceeds to manipulate, with the other hand, the row of elements on the other stringer into the guide channel in the presser foot. The presser foot with the pair of stringers manually supported thereunder is then lowered onto the fabric which has been placed over the throat plate on the bed of the sewing machine.
Thus, according to the prior art device, the fastener stringers are deposited onto the fabric on the throat plate after having their rows of elements manipulated into the respective guide channels in the presser foot. It requires utmost skill on the part of the operator to speedily and properly install the fastener stringers between the presser foot and the fabric on the throat plate bacause the operator is deprived of his view of the stringers by the presser foot.
The fastener stringers placed in the above described manner between the presser foot and the fabric on the throat plate are usually in need of readjustment as to their longitudinal positions with respect to each other. For this readjustment the operator must first raise the presser foot, by operating its control lever with one of his hands, only to such an extent that the guide channels in the foot will not disengage the rows of elements, and he uses the other hand to readjust the longitudinal positions of the fastener stringers one with respect to the other.
The operator has heretofore been required to follow such a troublesome procedure preparatory to stitching of each pair of concealed fastener stringers to a fabric. Simplification of this preparatory procedure is certain to result in material enhancement of the efficiency with which pairs of concealed fastener stringers are machine sewn onto successive pieces of fabric.